1. Field of the Invention
The present invention relates to a lensed optical fiber, a process for production and apparatus for production of the same, and a laser diode module.
2. Description of the Related Art
Among laser diode modules, there are types which input light emitted from a laser diode into an optical fiber.
As a lensed optical fiber used for such a laser diode module, for example, there is known an optical fiber with an entire front end formed into a convex lens shape (see U.S. Pat. No. 3,910,677).
A laser diode module comprised of such a lensed optical fiber and laser diode optically coupled together is used for example as the excitation light source of an erbium doped fiber amplifier (EDFA) or Raman amplifier.
A laser diode module able to be used as such an excitation light source is required to give an extremely high light output compared with a communications use light source. This requirement is being increasingly severe with each passing year such as from at least 100 mW to at least 200 mW, at least 300 mW, etc.
In such a conventional laser diode module using a lensed optical fiber, however, the ratio of the amount of light input to the lensed optical fiber in the entire output of light from the laser diode, that is, the coupling efficiency of the laser diode and lensed optical fiber, is only about 80 percent. It has been difficult to achieve a coupling efficiency higher than that. Therefore, in conventional laser diode modules using lensed optical fibers, it has been difficult to obtain a high light output.
An object of the present invention is to provide a lensed optical fiber superior in coupling efficiency with a laser diode, a process of production and apparatus for production of the same, and a laser diode module.
According to a first aspect of the present invention, there is provided a lensed optical fiber comprised of an optical fiber having a core and a cladding and a lens portion formed on its front end, the lens portion having a substantially flat portion formed at an end face of the core, slanting faces formed at an end face of the cladding, and convex curved faces including part of the core formed between the substantially flat portion and slanting faces.
As one example, the lens portion is formed shaped as a wedge.
As another example, the lens portion is formed shaped as a cone with a top cut away.
Preferably, a width or diameter of the substantially flat portion is 0.2 to 0.6 time a core diameter.
Preferably, a width or diameter of the substantially flat portion is at least 1 xcexcm.
Preferably, the substantially flat portion has an average radius of curvature of at least 10 times the radii of curvature of the convex curved faces.
Preferably, a center portion of the substantially flat portion is comprised of a planar portion not formed into a curved face.
Preferably, a width or diameter of the planar portion is at least 0.5 time a diameter or width of the substantially flat portion.
Preferably, the planar portion is a mirror face formed by cleavage.
According to a second aspect of the present invention, there is provided a process of production of a lensed optical fiber comprising a step A of forming a planar portion substantially perpendicular to a core center axis at a front end of an optical fiber, a step B of forming slanting faces around the planar portion, and a step C of processing ridge portions of the planar portion and the slanting faces to form convex curved faces and finishing the planar portion to a substantially flat portion.
Preferably, step A is a step of cleaving the optical fiber to form a planar portion comprised of a cleaved face.
Preferably, step A is a step of polishing an end face of the optical fiber to form a planar portion.
Preferably, step B is a step of forming the slanting faces so that widths xcex41 and xcex42 between the core and the ridges of the slanting faces at the planar portion become ⅓ to 3 times a diameter Dcr of the core.
Preferably, step B is a step of forming two slanting faces at the two sides of the planar portion.
Preferably, step B is a step of polishing the optical fiber while turning it about a core center axis.
Preferably, the process further comprises temporarily holding a plurality of optical fibers by inserting them into a holder formed with a row of a plurality of optical fiber holes and processing the plurality of optical fibers all together by at least one of the step A, step B, and step C.
Preferably, the process further comprises temporarily holding a plurality of optical fibers by inserting them into a holder formed with a row of a plurality of optical fiber holes, processing them all together by the step A and step B, then processing the plurality of optical fibers one by one by step C.
Preferably, the process further comprises temporarily holding a plurality of optical fibers by inserting them into a holder formed with a row of a plurality of optical fiber holes and polishing the plurality of optical fibers together with the holder by at least one of the step A, step B, and step C.
Preferably, the step B and/or step C is a step of running a polishing tape and bringing the polishing tape into contact with a desired processing portion of the optical fiber.
Preferably, step C is a step of running a polishing tape abutting at its back against a back member having a groove and bringing the polishing tape into contact with ridge portions between the planar portion and slanting faces of the optical fiber.
According to a third aspect of the present invention, there is provide an apparatus for production of a lensed optical fiber, comprising a holder for holding an optical fiber, a polishing tape, a drive mechanism for running the polishing tape, and a back member having an abutting face for abutting against a back surface of the polishing tape.
Preferably, the polishing tape is arranged at the two sides of the holder.
Preferably, the back member is provided with a groove in its abutting surface.
According to a fourth aspect of the present invention, there is provided a laser diode module comprising a laser diode and a lensed optical fiber optically coupled with the laser diode.
The light emitted from the laser diode, as shown in FIG. 18, is strongest at the portion of the optical axis.
The lensed optical fiber of the present invention has a substantially flat portion formed at its front end, so can receive this strongest light efficiently. Further, the lensed optical fiber of the present invention has convex curved faces formed between the substantially flat portion and slanting faces and is therefore raised in lens effect.
Therefore, according to the lensed optical fiber of the present invention, it is possible to receive light emitted from the laser diode with an extremely high coupling efficiency.
These and other objects, features, and advantages of the present invention will become clearer from the following detailed description of the preferred embodiments given with reference to the attached drawings.